Tire parameters of a motor vehicle such as tire pressure, temperature, but also the frictional connection between the tire and the road surface are decisive values for the safety and road handling control for motor vehicles. Because of the high relevance of this topic, numerous remedies were developed in the past for tire sensors and the relationships between tire pressure, tire temperature, stress value, elongation value and the coefficient of friction, frictional connection, road surface texture, rolling friction, aquaplaning, etc. intensively discussed. Basic information can be found in, for example, DE 3937966 A1, DE 4242726 A1 and W. F. Kern: “Über Verformungsmessung an Kfz Reifen mittels spezieller Dehnungsmesser” (about deformation measurement on motor vehicle tires by means of a special extensometer), Automobiltechnische Zeitschrift ATZ, 63 (1961) pp. 33et seq.
In general, sensors have an electrical cable connection through which the sensor is supplied with energy and through which the measured values of the sensor are relayed electrically. In general, for tire sensors such a remedy is unsuitable because the rotation would require slip rings or similar devices for conduction through a cable. Therefore, the sensor values of tire sensors are usually transmitted via radio from the site of the measurement to a remote evaluation unit.
However, many well-known radio sensors have a considerable disadvantage: They need a battery or similar energy sources for which procurement and especially maintenance gives rise to considerable costs or dangers (leakage of battery acids, out-of-balance, etc.). The use or the service life of batteries is often also limited by the environmental conditions (e.g. very high or low temperatures).
Characteristic for a wheel is that it has parts that rotate when moving and that these rotations:                cause, on the one hand, both vibrations and sound and/or ultrasound signals in the bearings and/or at the points of contact wheel/road surface,        and, on the other hand, the rotation leads to mechanical forces and deformations of, for example, the tire.        
Therefore, these two mechanical energy forms, at least as soon as the vehicle starts moving, are available at the location or in the vicinity of the location where the tire sensor is to operate.
A sound converter or a piezoconverter can convert this acoustic or mechanical energy to an electrical alternating signal. According to the invention, this energy is used for operating one or more sensors that transmit their state or status transition via radio.
Furthermore, radio sensors self-sufficient in terms of energy are also well-known from the prior art in which the available mechanical energy is used to operate a radio sensor. In principle, the use of piezoelectric elements is also known for this purpose.
Wireless, passive quartz sensors for tire measuring devices are known from R. Grossmann: “Wireless Measurement of Tire Pressure with Passive Quartz Sensors”, Proceedings of the SPIE, SPIE Vol. 3670, pages 214 to 222, Newport Beach, 1999.